<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .box {
            width: 300px;
            height: 100px;
            background-color: pink;
            margin: 100px 200px;
        }
        .red,.green,.blue{
            float: left;
            width: 100px;
            height: 100px;
            background-color: red;
        }
        .green{
            background-color: green;
        }
        .blue{
            background-color: blue;
        }
    </style>
</head>

<body>
    <div class="box">
        <div class="red">1</div>
        <div class="green">2</div>
        <div class="blue">3</div>
    </div>
</body>

</html>